Method for operating a drive train of a motor vehicle, and drive train module of a motor vehicle of this type

Abstract

A method for operating a drive train of a motor vehicle, the drive train having at least one transmission ( 2 ) for carrying out different transmission gear ratios between an input shaft ( 21 ) and an output shaft ( 22 ) of the transmission ( 2 ) by selectively engaging hydraulically actuatable shift elements of the transmission (G), the drive train further having an electric machine as a drive source ( 1 ), and a hydraulically actuatable or bridgeable starting component ( 3 ) in the power path between the drive source ( 1 ) and the output shaft ( 22 ). The method includes performing a starting process of the motor vehicle driven solely by the drive source ( 1 ) with an engaged or bridged starting component ( 3 ). The method further includes limiting a drive source torque ( 1 t ) during the starting process to a maximum value dependent on a current system pressure ( 2 p ) of a hydraulic system of the transmission ( 2 ).

The invention claimed is: 
     
       1. A method for operating a drive train of a motor vehicle, the drive train having at least one transmission ( 2 ), the transmission ( 2 ) configured such that different gear ratios between an input shaft ( 21 ) and an output shaft ( 22 ) of the transmission ( 2 ) are made available by selectively engaging hydraulically actuatable shift elements of the transmission (G), the drive train further having an electric machine as a drive source ( 1 ) and a hydraulically actuatable or bridgeable starting component ( 3 ) in a power path between the drive source ( 1 ) and the output shaft ( 22 ) of the transmission (G), the method comprising:
 performing a starting process of the motor vehicle, the starting process driven solely by the drive source ( 1 ) with the starting component ( 3 ) locked-up; and 
 limiting a drive source torque ( 1   t ) of the drive source ( 1 ) during the starting process to a maximum value of the drive source torque ( 1   t ), the maximum value of the drive source torque ( 1   t ) being dependent on a current system pressure ( 2   p ) of a hydraulic system of the transmission ( 2 ). 
 
     
     
       2. The method of  claim 1 , wherein the maximum value of the drive source torque ( 1   t ) is additionally dependent on a gear ratio engaged in the transmission ( 2 ). 
     
     
       3. The method of  claim 1 , wherein the maximum value of the drive source torque ( 1   t ) is additionally dependent on a temperature of a hydraulic fluid of the transmission ( 2 ). 
     
     
       4. The method of  claim 1 , wherein the maximum value of the drive source torque ( 1   t ) is additionally dependent on a temperature of a shift element ( 3   x ) of the transmission ( 2 ). 
     
     
       5. The method of  claim 1 , wherein the transmission ( 2 ) includes a first pump ( 26 ) drivable by the drive source ( 1 ) and a second pump ( 24 ) drivable independently of the drive source ( 1 ), the first and the second pumps ( 26 ,  24 ) are configured for supplying pressure to the shift elements and the starting component ( 3 ) or to the shift elements and a lock-up clutch of the starting component ( 3 ), the method further comprising:
 determining an output pressure of the first pump ( 26 ) with a first pressure model, and an output pressure of the second pump ( 24 ) with a second pressure model; and 
 utilizing the greater of the output pressure of the first pump ( 26 ) and the output pressure of the second pump ( 24 ) as the current system pressure for limiting the drive source torque ( 1   t ). 
 
     
     
       6. The method of  claim 1 , wherein the starting component ( 3 ) is transferred into a slip state when the drive source torque ( 1   t ) of the motor vehicle reaches or exceeds the current maximum value of the drive source torque ( 1   t ). 
     
     
       7. The method of  claim 6 , wherein a rotational speed of the drive source ( 1 ) is increased in parallel with the transfer of the starting component ( 3 ) into the slip state. 
     
     
       8. A drive train module of a motor vehicle, comprising:
 at least one drive source ( 1 ), the at least one drive source ( 1 ) being an electric machine; 
 an interface to an internal combustion engine ( 9 ) of the motor vehicle; 
 a control unit; 
 a transmission (G) configured for providing different gear ratios between an input shaft ( 21 ) and an output shaft ( 22 ) of the transmission ( 2 ) by the selective engagement of hydraulically actuatable shift elements of the transmission (G); and 
 a hydraulically actuatable or bridgeable starting component ( 3 ) in a power path between the drive source ( 1 ) and the output shaft ( 22 ) of the transmission (G), 
 wherein the control unit is configured for, by an open-loop control system,
 performing a starting process of the motor vehicle, the starting process driven solely by the drive source ( 1 ) with the starting component ( 3 ) locked-up, and 
 
 limiting a drive source torque ( 1   t ) of the drive source ( 1 ) during the starting process to a maximum value of the drive source torque ( 1   t ), the maximum value of the drive source torque ( 1   t ) being dependent on a current system pressure ( 2   p ) of a hydraulic system of the transmission ( 2 ).